What process allows carbon dioxide to move from the capillaries into the alveoli?

The movement of carbon dioxide from the capillaries into the alveoli is primarily accomplished through the process of diffusion. This process occurs because of the concentration gradient that exists between the blood in the capillaries and the air in the alveoli.

In the capillaries, carbon dioxide levels are higher due to cellular respiration occurring in the tissues, where carbon dioxide is produced as a waste product. In contrast, the concentration of carbon dioxide in the alveoli is lower because it is continuously being removed from the lungs when you exhale.

As a result of this concentration difference, carbon dioxide molecules naturally move from an area of higher concentration (the blood in capillaries) to an area of lower concentration (the air in the alveoli) until equilibrium is reached. This passive process does not require energy, which is why diffusion is the correct mechanism for the movement of carbon dioxide in this context.

Active transport, exocytosis, and filtration do not apply here because they involve processes that either require energy or pertain to larger particles or fluids, rather than the passive movement of gas molecules across a membrane based on concentration gradients.